The present invention relates to a mass analyser and a method of mass analysing ions.
It is often necessary to transfer ions from an ionisation region of a mass spectrometer which may be maintained at a relatively high pressure to a mass analyser which is maintained at a relatively low pressure. It is known to use one or more Radio Frequency (RF) ion guides to transport ions from the ionisation region to the mass analyser. It is known to operate the RF ion guides at intermediate pressures of about 10−3-1 mbar.
It is also known that the time averaged force on a charged particle or ion in the presence of an inhomogeneous AC or RF electric field is such as to accelerate the charged particle or ion to a region where the electric field is weaker. A minimum in the electric field is commonly referred to as a pseudo-potential valley or well. Known RF ion guides exploit this phenomenon by arranging for a pseudo-potential valley or well to be generated or created along the central axis of the RF ion guide so that ions are radially confined centrally within the RF ion guide.
Known RF ion guides are used as a means of efficiently confining and transporting ions from one region to another. The potential profile along the central axis of known RF ion guides is substantially constant and as a result known RF ion guides transport all ions with minimum delay and without discrimination between ions of different species.
It is desired to provide an improved mass analyser.